Exercise treadmills are widely used for various purposes. Exercise treadmills are, for example, used for performing walking or running aerobic-type exercise while the user remains in a relatively stationary position. Further exercise treadmills are used for diagnostic and therapeutic purposes. For all of these purposes, the person on the exercise treadmill normally performs an exercise routine at a relatively steady and continuous level of physical activity. Examples of such treadmills are illustrated in U.S. Pat. No. 4,635,928, 4,659,074, 4,664,371, 4,334,676, 4,635,927, 4,643,418, 4,749,181, 4,614,337 and 3,711,812.
Exercise treadmills typically have an endless running surface which is extended between and movable around two substantially parallel pulleys at each end of the treadmill. The running surface may be comprised of a belt of a rubber-like material, or alternatively, the running surface may be comprised of a number of slats positioned substantially parallel to one another attached to one or more bands which are extended around the pulleys. In either case, the belt or band is relatively thin. The belt is normally driven by a motor rotating the front pulley. The speed of the motor is adjustable by the user so that the level of exercise can be adjusted to simulate running or walking as desired.
The belt is typically supported along at least its upper length between the pulleys by one of several well-known designs in order to support the weight of the user. For example, rollers may be positioned directly below the belt to support the weight of the user. Another approach is to provide a deck or support surface beneath the belt, such as a wood panel, in order to provide the required support. Here a low-friction sheet or laminate is usually provided on the deck surface to reduce the friction between the deck surface and the belt. Because the belt engages the deck surface, friction between the belt and the deck arises and the belt is therefore subject to wear. Further, most of the decks are rigid resulting in high impact loads as the user's feet contact the belt and the deck. This is often perceived by users as being uncomfortable and further can result in unnecessary damage to joints as compared to running on a softer surface.
Because the typical treadmill has a very stiff, hard running surface and can become uncomfortable for extended periods or running, some manufacturers have applied a resilient coating to the running surface, such as rubber or carpeting, to reduce foot impact. Unfortunately, these surfaces for the most part have not provided the desired level of comfort because the running surface tends to retain its inherent stiffness. Attempts to solve this problem by using a thicker belt to provide a more shock absorbent running surface have not been successful for the reasons given in U.S. Pat. No. 4,614,337. Specifically, the thickness of the belt has to be limited in order to limit the belt drive power to reasonable levels. In other words, the thicker the belt, the more power that is required to drive the pulley. To keep motor size cost effective, it has been necessary to keep the belt relatively thin. As discussed below, the power of the motor required to drive a pulley is also related to the size of the pulleys.
Pulleys used in current exercise treadmills typically are made of steel or aluminum and as such are relatively expensive to make and are relatively heavy. Therefore, because of tooling, manufacturing and material costs, the diameter of the pulleys are normally no larger than three to four inches.
Additionally, the diameter of the pulley directly affects the power required to rotate the pulley as does the thickness of the belt. If the diameter of the pulleys is relatively small, the thickness of the belt must be kept relatively thin. As the diameter of the pulley is increased, the belt may be made thicker for the same amount of power available to drive the pulleys. As discussed above, the thicker the belt, the more shock the belt will absorb.
A further disadvantage of smaller pulleys results from the fact that the reduced surface area of the pulley contacting the belt requires increased tension in the belt in order to transfer torque from the treadmill motor to the belt. In some cases, this increased tension can result in decreased belt life.
The pulleys used in current exercise treadmills are typically of a "convex" or of a "cambered" design and as such have a substantially inwardly sloping profile with a portion of the pulley having a larger diameter, or crown, at the center. The convex-type pulley has a rounded crown at its center portion and the cambered-type pulley has a cylindrical center section between conical ends. The purpose of using these two types of pulleys is to maintain "tracking" of the belt felt because the belt is less likely to slide from side to side on the pulley during rotation if the pulley has a crown. Unfortunately, belts on convex- or camber-type pulleys also tend to be sensitive to improper adjustment and side loading, which can occur when the user is not running on the center of the belt.
Another source of belt wear on existing exercise treadmills results from driving the front belt pulley instead of the rear belt pulley. In a front drive arrangement, the belt has a tendency to develop a slack portion on the upper or running surface of the belt. This tends to increase belt wear. Because existing treadmills have relatively small diameter belt pulleys, it has not been practical to locate the drive motor such that the rear belt pulley can be driven by the motor.
Because most pulleys use the convex- or camber-type configuration as a belt guide, the belts are still sensitive to improper adjustment and side loading. A system whereby a more positive, lateral "tracking" or guidance of the belt is achieved during rotation is therefore desirable.
Many current exercise treadmills also have the ability to provide a variable incline to the treadmill. Normally, the entire apparatus is inclined, not just the running surface. There are a number of exercise treadmills having manual or power driven inclination systems to take advantage of the fact that the exercise effort, or aerobic effect, can be varied greatly with small changes in inclination. For example, a seven percent grade doubles the aerobic or cardiovascular effort compared to level walking or running exercise.
Current inclination or lift mechanisms typically comprise a toothed post in a rack-and-pinion arrangement or a threaded post on which a sprocket attached to the treadmill frame is rotated upwards to lift the treadmill. In both arrangements, the post must be at a height equivalent to the height of travel of the treadmill frame to accommodate the travel of the pinion or sprocket. The length of the post tends to compromise the aesthetics of the treadmill because the post has to extend beyond the plane of the running surface to provide the desired inclination of the running surface. Therefore, a lift mechanism with a large extension ratio which would fit primarily within the treadmill enclosure is desirable.
The treadmill user's stride also effects the user's body because the resultant force on the user's body increases as the stride increases. If the user is running relatively hard, especially over an extended period of time, physical damage to the user's feet and legs can occur. The larger the resultant force the greater the likelihood of physical damage. If a user's stride results in a force (measured in pounds) which is about equal to or greater than twice the user's body weight, the force can be considered excessive. Therefore, a sensor which could measure the force or impact on the treadmill by a user is desirable.